Answer: 
=========================================================
Explanation:
Use the pythagorean trig identity
and plug in the fact that 
Isolating sine leads to
. I'm skipping the steps here, but let me know if you need to see them.
The result is negative because we're in quadrant 4, when y < 0 so it's when sine is negative.
Therefore,

Answer:
<u>After July, Ana's monthly salary was $1920</u>
Step-by-step explanation:
In May, Ana's monthly salary was $2000. During the next month, the salary increased by 20%, or (0.2)(2000)

So, in June, Ana's monthly salary was $2400. During the next month, the salary decreased by 20%, or (0.2)(2000)

Therefore, after the two changes, Ana's monthly salary was <u>$1920</u>
Answer:
<em><u>x=9, y=12</u></em>
Step-by-step explanation:
-5x+4y=3
--------A
x=2y-15----------B
Putting the value of x from B in A
-5(2y-15) +4y=3
-10y+75+4y=3
-6y=3-72
-6y=-72
y=72/6= 12
Putting the value of y =12 in B
x= 2(12)-15
x= 24-15
x=9
Answer:
$1.30
Step-by-step explanation:
Let x = the cost of the pencil
Let x + .80 = the cost of the pen
Let 4(x + .80) = the cost of the binder
x + x + .80 + 4(x + .80) = 11.80
2x + .80 + 4x + 3.20 = 11.80
6x + 4.00 = 11.80
6x = 7.80
x = $1.30
x + .80 = $2.10
4(x + .80) = $8.40